1992 Johnson 120 tland

[michaelhedges]

I have the above engine on a 17' stratos fish and ski. A few years ago we lost a lot of horse power. Top end and fuel economy went to crap. Brought motor to three different mechanics with not much luck. Over this time period the boat has not been used much, maybe 2hrs a year on a small lake. I started to want to try to get the motor back into shape, so I got a repair manual from the liberary and started to work. Replaced VRO, plugs, plug wires, and battery charger(can't think of the name) water pump, did a link and sync and adjusted timing. All needed replacement per test in manual. Used sea foam in about 18 gallons of fuel on trips to small lake. All cylinders have between 130 and 135 lbs of compression. Took boat out last week and I did see a considerable increase in hp and mileage. I got around 3 to 3.5mpg. When the loss in hp began and with no luck at the repair shops, we had the prop repitched to a 19 in stead of a 22. We could turn the 22 raker at 5600 and around 55mph. With the 19 and the improved running condition of the motor we still have prop blow out at around 52-5300 rpm. We do however run much better on the top end, around 45. The boat just doesn't like to get on pad much. I looked at the carbs and saw very simple carb with not much to go wrong with it as too jets. From what I can tell the carbs have on main plastic jet that all the fuel passes through to the intake. Is this correct or am I missing a lot? I also would like to know if this is the case and all is clean would I get anything out of new carbs or should I run something in the fuel to clean something that I can not see?(This is the original carbs and if something could be wrong is their something I could look at to see what is wrong?) What else could be my problem?

 

[angus63]

Re: 1992 Johnson 120 tland

Have you messed with motor height? Shouldn't blow out at 5200. Where is the cavitation plate in relation to the bottom/transom intersection?

 

[michaelhedges]

Re: 1992 Johnson 120 tland

Motor is on lowest bolt holes possible.

 

[angus63]

Re: 1992 Johnson 120 tland

it sounds to me like either a setup issue(height,prop,setback,etc...) or the lack of use (water in fuel, gummed up carbs/jets, varnished fuel, etc...) Running on a fresh tank of fuel and carb rebuild would be my first effort. Maybe Mr. Dhadley will chime in with setup advice.

 

[ezeke]

Re: 1992 Johnson 120 tland

Your carburetors each have three jets [Orifices] none are made of plastic. There are a low speed air, an intermediate, and a high speed. You can see the location of each part in the carburetor diagram for your motor:

http://epc.brp.com/default.aspx?brands=ej&lang=e

Pictures of your setup, especially one showing the location of the anti- ventilation plate in relationship to the keel, would help the setup experts to understand your problem. Unfortunately, the fact that you are on one set of bolt holes or another will tell them nothing.

 

[michaelhedges]

Re: 1992 Johnson 120 tland

I can't get a picture file size small enough to post so if you need a picture I will gladly send one to you via email.

Thanks
Michael

 

[michaelhedges]

Re: 1992 Johnson 120 tland

I appreciate the help everyone. I have another question. I did not follow the decarb procedure correctly, so I did it again today. The questions I have are when you run the motor with the solution should the engine be in gear or in neutral? I did it with the motor in gear and ran out of solution in 5min.

Is this correct?

Michael

 

[reeldutch]

Re: 1992 Johnson 120 tland

why do you want to decarb if your compression is 130 to 135 on all 4?

what do you mean with blow out??

may be you got a spun hub????

 

[michaelhedges]

Re: 1992 Johnson 120 tland

I wanted to try to decarb because of possible loss in power. With two people on board and equipment, the prop blows out at around 5200rpm's. You can fell the front of the boat take a dive down bacj to the water. This is a 92 model motor that has operated flawlessly until this problem arose and has never been decarbed.

Thanks,

Michael

 

[Brew2]

Re: 1992 Johnson 120 tland

I like where reeldutch was going. When you say "Blow out", are you saying that the prop is leaving the water resulting in your power loss or are you just saying you just have a power loss. If the latter, the hub on your prop may be "giving out" at higher RPMs resulting in the power loss (ie. a spun hub).

You can check for this by marking the prop and hub with some sort of waterproof marker, run the motor until you get the power loss, then check and see if the mark on the hub has moved relative to the mark in the prop. If so, you will need to replace the hub on your prop or get a new prop.

Good luck.

 

[michaelhedges]

Re: 1992 Johnson 120 tland

Wouldn't the hub get worse and worse?